Safety Issues

Zinc taken orally seldom causes any immediate side effects other than occasional stomach upset, usually when it's taken on an empty stomach. Some forms do have an unpleasant metallic taste. Use of zinc nasal gel, however, has been associated with anosmia (loss of sense of smell).
1 In fact, After receiving over 130 reports of anosmia, the FDA warned consumers and healthcare providers in 2009 to discontinue use of certain Zicam Cold Remedy intranasal zinc-containing products, including Zicam Cold Remedy Nasal Gel, Cold Remedy Nasal Swabs and Cold Remedy Swabs in kids size.
2 Furthermore, if the gel is inhaled too deeply, severe pain may occur.

Long-term use of oral zinc at dosages of 100 mg or more daily can cause a number of toxic effects, including severe copper deficiency, impaired immunity, heart problems, and anemia.
345 Zinc at a dose of more than 50 mg daily might reduce levels of HDL ("good") cholesterol.
6 In addition, very weak evidence hints that use of zinc supplements might increase risk of prostate cancer in men.
7
The US government has issued recommendations regarding "tolerable upper intake levels" (ULs) for zinc. The UL can be thought of as the highest daily intake over a prolonged time known to pose no risks to most members of a healthy population. The ULs for zinc are as follows:
8

Infants

0-6 months: 4 mg

7-12 months: 5 mg

Children

1-3 years: 7 mg

4-8 years: 12 mg

9-13 years: 23 mg

Males and Females

14-18 years: 34 mg

19 years and older: 40 mg

Pregnant Women and Nursing Women

18 years or younger: 34 mg

19 years and older: 40 mg

There are also some interactions between zinc and certain medications to consider:

Use of zinc can interfere with the absorption of the drug penicillamine and also antibiotics in the tetracycline or fluoroquinolone (Cipro, Floxin) families.
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The potassium-sparing diuretic amiloride was found to significantly reduce zinc excretion from the body.
14 This means that if you take zinc supplements at the same time as amiloride, zinc accumulation could occur. This could lead to toxic side effects. However, the potassium-sparing diuretic triamterene does not seem to cause this problem.
15

Penicillamine : Zinc interferes with penicillamine's absorption so it may be advisable to take zinc and penicillamine at least 2 hours apart.

Zinc supplements: You should also take extra
copper and perhaps
magnesium as well because zinc interferes with their absorption. Zinc interferes with
iron absorption, too, but you shouldn't take iron supplements unless you know you are deficient.